Trapping of fast magnetoacoustic waves close to an X line in a toroidal system

The trapping of fast magnetoacoustic waves around the X line of a toroidal magnetic configuration is investigated in the framework of ideal magnetohydrodynamics using a WKB approach. The frequency spectrum and the relevant eigenmodes are determined for the hyperbolic case, and for a divertorlike geometry. Striking differences are pointed out, which are due to the breaking of the symmetry in the system.